Brinell Hardness Testing
The Brinell hardness test method, as defined in ASTM E10, test the samples whose structure or surface is either coarse or rough including forgings and castings. It has a high-test load (3000 kgf) and a 10mm diameter indenter, where the resultant indentation averages out the surface and sub-surface irregularities.
The Brinell method employs a predetermined test load (F) into a carbide ball of fixed diameter (D) held for a fixed time period and removed. The resultant impression can be measured using a customized Brinell microscope or optical system across a minimum of two diameters at right angles to each other after which these results are averaged (d). Though the calculation mentioned below can derive the Brinell number, a chart is used to convert the averaged diameter to a Brinell hardness number.
The test forces used for non-ferrous materials range from 500kgf up to 3000kgf for cast iron and steels. There are varied other Brinell scales where the load is as low as 1kgf with the indenter diameter of 1mm diameter, but they are infrequently used.
Does the mention of Brinell Hardness Testing throw you off sometimes?
Materials have different properties used to measure specific operational requirements and suitability. One of such properties is material hardness, often used to measure a material’s ability to withstand some applied forces. Material hardness is also measured to ascertain the material’s suitability for manufacturing applications such as welding. But the correct method to measure different materials’ hardness is often a challenge as numerous material hardness testing methods are available today. Brinell hardness testing is one of the most popular hardness testing methods used across various industries because it provides numerous benefits and has many applications. This article will help you understand the process and advantages of using the Brinell hardness test.
I. What is the Brinell Hardness Test?
While material hardness has been an essential criterion for many industrial processes, testing this property has always been challenging. Many techniques have been developed over the years to ascertain material hardness for various materials. However, the Brinell hardness testing method has been one of the earliest and most accurate methods that were generally adopted by various industries for metals.
The two-step method involves first applying a load or a combination of loads with a spherical indenter. This indenter is usually 10mm in diameter, but other indenters with different diameters can also apply various combinations of forces to the material surface. The second step in the test is the magnification and measurement of the indentation, then using a necessary formula to calculate the Brinell hardness number. The formula is the force applied per unit area of indentation observed. This Brinell hardness is often standardized or converted to other hardness numbers using specific conversion tools and tables.
II. Advantages of Brinell Hardness Test
Brinell hardness test offers many benefits for different materials and applications, especially in the metallurgy and manufacturing industries. Some of the most important advantages include:
- An irregular or complex geometrical surface does not affect the accuracy of a Brinell hardness test.
- It is less sensitive.
- Cast materials and powder metallurgy components’ hardness can be measured using the Brinell test.
- It offers high resistance to accommodate heavy loads.
- It is easy to accurately view indentation using a microscope.
III. Application of Brinell Hardness Test
Brinell hardness test has wide applications in the metal forging and manufacturing circles, where it is used for ascertaining the tensile strength of metals. Since the range of applied force ranges from low to high, the Brinell hardness test can be applied to metals like copper and aluminum using low forces and cast irons and steel with higher force. Also, the application of high loads, which is responsible for large indents on the material, makes Brinell hardness testing most suitable for situations where variations exist for surface conditions, such as large casting and forging large components, which makes other techniques impossible.
The Brinell hardness testing machine is designed to accommodate large components and parts, making it possible to test large piping and engine parts that require large indentation. It is also applicable for testing materials with a minimum thickness of eight times the depth tested due to its large indentation possibilities.
IV. How to Conduct a Brinell Hardness Test?
Conducting a Brinell Hardness Test follows the guidelines in ASTM E10, which specifies its suitability for coarse-grained or rough-surfaced material that can’t be tested accurately using other techniques.
With a force of 3000 kgf and an indentation of 10mm diameter Brinell hardness test often provides an indentation that resolves many inconsistencies for material surfaces.
Firstly, a force (F) using a predetermined weight of a circular ball with a fixed diameter (D) is applied to the material surface after being held for a period. A measurable indentation occurs on the material surface, and a Brinell microscope is used in its measurement using a minimum of two diameters perpendicular to each other. The average of this indentation measurement is taken as (d). A standard chart with average indentation sizes and corresponding Brinell hardness numbers ensures that you can accurately generate the required Brinell hardness number for the test.
Furthermore, the Brinell hardness test can also measure the hardness of non-ferrous materials using 500kgf while steel and cast-iron materials use 3000 kgf.
V. How to Measure Brinell Hardness?
Before you begin measuring the Brinell hardness of a material, you need to carry out the following steps:
- The test material’s surface must be well cleaned before the test.
- Choose the appropriate indenter for the test.
- Raise the test table to the desired elevated position.
The test starts by releasing a steel ball with a diameter ‘D’ under a force of ‘F’ onto the test material. You time this process for a long time and measure the mean diameter ‘d’ of the impression left on the surface. Calculate the BHN (Brinell Hardness Number) as load divided by the indentation’s surface area.
The indentation’s depth h = 0.5[D/(D2-d2)] and the BHN = F/πDh
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